CHAPTER XVI 

 POTATO IMPROVEMENT 



Potatoes have been generally introduced into cultivation 

 since the discovery of America, and are now a crop of major im- 

 portance in many countries. The large number of varieties is an 

 illustration of the rapid development in domestic plants of varie- 

 ties which are suited to special soil and climatic conditions. As 

 potatoes are reproduced commercially by tubers, they furnish an 

 excellent illustration of the way in which vegetative reproduction 

 modifies breeding methods. 



Origin and Species. There are from five to 100 species of 

 tuber-bearing potatoes according to the number of forms which 

 are recognized as separate species (East, 19086: Wight, 1916). 

 Whether the cultivated potato arose from a single wild species or 

 from several is a debatable question. The preponderance of 

 opinion is that there is only a single wild species, Solanum tubero-, 

 sum L., which deserves to be considered as the stem form from 

 which all cultivated varieties arose. Wight (1916), after care- 

 fully examining herbarium material, previous records, and wild 

 species, makes the following statements: 



"Every reported occurrence of wild S. tuberosum that I have been 

 able to trace to a specimen, either living or preserved in the herbarium, 

 has proved to be a different species. I have not found in any of the 

 principal European collections a single specimen of Solanum tuberosum 

 collected in an undoubted wild state." 



Berthault (1911) cites Heckel, Planchon. and Labergerie as 

 examples of recent workers who believe that other wild species 

 gave cultivated S. tuberosum forms by mutation; Planchon be- 

 living that the original form was S. commersonii; Heckel that 

 S. maglia through mutation produced cultivated potatoes; while 

 Labergerie believed both of these species gave cultivated forms 

 through mutation. Berthault attempted to answer the question 

 by growing seeds and tubers of both these species and also by 

 growing seed of several cultivated varieties. Progeny of seed or 

 tubers of S. maglia and S. commersonii gave no forms which 



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